Method of making roll welded hollow sheet metal structure



July 17, 1956 ADF. JOHNSON 2,754,572

METHOD OF MAKING ROLL WELDED HOLLOW SHEET METAL STRUCTURE Filed July 14, 1954 3 Sheets-Sheet l IN VENTOR. ARTHUR F. JOHNSON MMW AGENT y 1956 A. F. JOHNSON 2,754,572

METHOD OF MAKING ROLL WELDED HOLLOW SHEET METAL STRUCTURE Filed July 14, 1954 5 Sheets-Sheet 2 IN VEN TOR.

ARTHUR F. JOHNSON BY clue 2a.

AGE/VI y 17, 1956 A. F. JOHNSON 2,754,572

METHOD OF MAKING ROLL WELDED HOLLOW SHEET METAL STRUCTURE Filed July 14, 1954 5 Sheets-Sheet 3 FIG. IO

IN VEN TOR. ART HLR F. JOHNSON United States Patent METHOD OF MAKING ROLL WELDED HOLLOW SHEET IVIETAL STRUCTURE Arthur F. Johnson, Boulder, Colo., assignor to Olin Mathieson Chemical Corporation, a corporation of Virginia Application July 14, 1954, Serial No. 443,277

9 Claims. (Cl. 29157.3)

This invention relates generally to metal fabrications and more particularly to an improved method for making hollow articles such as heat exchangers from sheet metal.

It has been proposed heretofore to manufacture hollow metal articles such as heat exchangers, structural members, airplane propellers and the like from sheet metal by a forge-welding process. Long, for example, in U. S. Patent 2,662,273 discloses such a process for making heat exchangers from superposed weldable sheets of metal. In such a process, a pattern of weld-preventing of stopoif material is sandwiched between adjacent surfaces of superposed sheets of metal and the adjacent surfaces of the superposed sheets not separated by the stop-off material are thereafter welded by hot rolling. Channels are then formed in the structure by expanding the unwelded areas by means of fluid pressure. Heretofore, it has been the practice to form such an article from a plurality of sheets of metal and, in order to prevent relative slippage between the sheets, the assembly has been spot welded at various places bordering the pattern of stopoff material before the assembly is hot rolled. By spot welding the assembly in several places, it is possible to prevent relative slippage between the sheets but such a process adds to the cost expense and is time consuming.

It is therefore an object of this invention to provide a novel and improved method for making hollow articles from sheet metal. Another object of this invention is to provide an improved process for forming hollow articles from metal by a forge-welding process. A further and more specific object of this invention is to provide a novel method for preventing relative movement of superposed plies of sheet metal during welding by a hot rolling process.

Other objects will become apparent from the following description with reference to the accompanying drawing in which 7 Figure 1 is a perspective view illustrating a sheet of metal treated in accordance with an embodiment of this invention and ready for application of stop-ofi material;

Figure 2 is a perspective view of the sheet of metal shown in Figure l tur'ned over 180 degrees and having a pattern of stop-off material applied to the surface thereof;

Figure 3 is a perspective view illustrating one embodiment of the invention ready for forge welding;

Figure 4 is a plan view of the end of the embodiment shown in Figure 3; V

Figure 5 illustrates a heat exchanger such as can be formed from an assembly similar to that shown in Figure 3;

Figure 6 illustrates in perspective another embodiment of the invention having stop-off material applied to the surface thereof;

Figure 7 illustrates in a plan view the sheet of Figure 6 partially folded to form a plurality of plies of metal;

Figure 8 is a plan View of the embodiment of a heat exchanger such as can be formed from an assembly similar to that-shown in Figure 6;

2,754,572 Patented July 17, 6

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Figure 9 illustrates another embodiment of this invention at the stage in the process where the sheet is partially folded; and

Figure 10 illustrates still another embodiment of the invention partially folded.

Generally speaking, the foregoing objects as well as others are accomplished in accordance with this invention by providing in a process which involves sandwiching a pattern of stop-off material between adjacent surfaces of metal sheets, forge welding those areas bordering the pattern and thereafter expanding the unwelded areas lying therebetween, the method of preventing relative movement between the various plies of such an assembly prior to and during forge-welding which involves bending a single sheet of metal into a plurality of layers thereof lying one over the other in face to face relationship. It has been found that adjacent plies of metal which are layers of a folded single sheet are stable against relative movement even when subjected to the thickness reducing pressures of a metal rolling mill. In practice, the thickness of metal sheets suitable for such a process is ordinarily too great to enable folding of the sheet without fracturing so a groove is formed in such sheet along the axis where it is to be folded prior to the bending and folding step in order to reduce the thickness of the sheet at this point. By this means fracturing of the sheet is avoided. Moreover, the groove facilitates folding of the sheet. The groove may be formed by any suitable means such as by milling or sawing. The groove depth required will vary with the thickness and physical properties such as, the elongation, of the sheet, it only being necessary that it be of such depth as to facilitate bending and to prevent the metal from fracturing during the bending operation.

From the foregoing general description, it should be apparent that the invention provides a combination of steps which is particularly advantageous in the manufacture of hollow articles from metal. By such a process, one sheet of metal is folded into a plurality of plies or layers lying in face to face relationship and this single sheet is then surface cleaned and otherwise prepared for forge-welding. Because of the bending process, the number of sheets which must be processed in making hollow articles is grossly reduced. A pattern of stop-off material is applied to the surface of the sheet so that each pair of face to face plies or layers after bending will have a pattern interspersed therebetween, and after the pattern has been dried or has been otherwise protected against smearing, the various plies are then formed by bending the sheet along predetermined lines. The assembly is thereafter forge-welded, such as by hot rolling in one pass, into a single sheet of metal having unwelded areas lying therein. The unwelded areas are later expanded by means of fluid pressure to form internal ducts or passageways in the structure.

In order better to describe and further clarify this invention, the following is a detail description of preferred embodiments thereof with reference to the accompanying drawings:

Referring to Figure 1, a groove 2 is formed by means of a suitable milling machine, planer, shaper or any other suitable device along the longitudinal axis at the center line of a preselected sheet of metal 1. Metal sheet 1 is about 0.2 inch thick and is composed of from about 92% to 94% copper, about 2.05% to 2.6% iron, about 0.025% phosphorus, with 0.05% lead, with the balance zinc and has awidth about twice that of the desired finished product. The length thereof is only about onehalf of the length desired in the final product. Groove 2, which divides sheet 1 into areas 3 and 4 of substantially equal widths, is preferably about 0.10 inch to 0.17 inch deep. 7

Sheet 1 is degreased by immersing it in an organic solvent bath such as naptha or white gasoline at room temperature and is then wiped free of solvent. The sheet is next immersed in an acid bath containing about 1 part 'of volume 68% nitric acid, one part by volume 95% sulfuric acid and one part by volume water at room temperature. This treatment removes any oxide film from the surface of the metal sheet. The sheet 1 is thoroughly rinsed to remove any acid clinging to the surface thereof and is air dried at room temperature. The surface of sheet 1 must be substantially chemically clean to insure good bonding in the subsequent forge-welding step.

A pattern of stop-off material is applied to area 3 as shown in Figure 2. It is to be noted that sheet 1 is turned over before the pattern 5 is applied so that.

the pattern is on the side opposite the groove 2. In other words, the pattern is applied to the underside of sheet 1 when it is in the position shown in Figure 1. Stop-off material 5 is composed of a mixture of about 13% colloidal graphite, about 40% calcium carbonate having a granulation of less than about 325 mesh, with the balance water. A silk screen is used for applying the stop-off material to the surface of sheet 1. After the stop-off material has dried sheet 1 is bent about 180 along the groove to superpose area 4 immediately above area 3, as illustrated in Figure 3, by means of a mechanical brake and a press. As illustrated in Figures 3 and 4, folded edge 6 projects from the assembly. Such a folded edge rigidly holds the two plies 3 and 4 against relative movement.

The resulting assembly formed from sheet 1 is placed in the furnace and heated to about 900 C. in a reducing atmosphere and, while at substantially this temperature, it is passed between the rolls of a rolling mill to reduce its thickness about 50% in a single pass. Those regions 9 of areas 3 and 4 not separated by the pattern of stopotf material 5 becomes forge-welded into a unitary structure. The pattern 5 of stop-off material, illustrated in Figures 2 and 3, elongates in the rolling process to the same extent as the sheet elongates as its plies 3 and 4 are forge-welded into one unitary structure. After cleaning by dipping in acid, rinsing in cold water and drying, the assembly is cold rolled to bring the length to that desired in the final product. The finished gauge after cold rolling is about 0.048 inch. The structure is then annealed at a temperature of about 750 C. for one-half hour and is thereafter cleaned by dipping in acid, rinsing in water and drying substantially as described hereinbefore in conjunction with previous steps of the process. The structure is next trimmed along its four edges to square up the product and to remove folded edge 6 therefrom.

The unwelded portion 8 which extends to the edge of the resulting structure is pried apart and a suitable tube 7, such as is illustrated in Figure 5, is driven into the opening. Fluid pressure is then applied through tube 7 to expand the unwelded areas to form a heat exchanger 9, such as illustrated in Figure 5.

In another embodiment of this invention, illustrated in Figure 6, two grooves 20 and 21 are formed in a single sheet of copper alloy 10 to divide it into three substantially equally dimensioned areas 11, 12 and 13. Suitable foreshortened patterns 14 and are placed on areas 11 and 13 respectively and the sheet of metal is thereafter bent to form the three layers represented as 11, 12 and 13 in Figure 7. Figure 7 illustrates the relative position of the three layers 11, 12 and 13 after they have been only partially bent. This structure is later pressed until the adjacent surfaces of 11 and 12 and 13 lie in face to face relationship with each other. It is to be noted that grooves and 21 are on opposite sides of sheet 10 and that likewise patterns 14 and 15 lie on opposite sides of the sheet with respect to each other as well as with respect to the adjacent grooves 20 and 21.

After the various layers 11, 12 and 13 of Figure 7 have been pressed until their adjacent surfaces contact each other, the assembly is forge-Welded by a hot rolling process such as described above. It is, of course, to beunderstood that the sheet is cleansed before the pattern is applied in accordance with a process similar to that described in the foregoing embodiment and that the assembly is heated to and is maintained at about 900 C. while it is rolled. After forge-Welding, the resulting. unitary structure is cleaned, cold rolled to the desired dimensions, annealed and trimmed to square up the structure and to remove the folded edges 43 and 16 in sub stantially thersame manner as described in the foregoing. embodiment illustrated in Figures 1 through 5. Those portions of the assembly which are separated by meansof the stop-off material and thus exist as unwelded areas are later expanded by means of fluid pressure after a suitable tube similar to 7, illustrated in Figure 5, has been inserted through the opening provided by the stopoff material extending to the edge of the sheet such as 17 and 18.

This embodiment is particularly advantageous for making a structure which can be a heat exchanger having conduits on each side thereof such as is illustrated in an end View in Figure 8. In such a device two separate fluids can be run through the channels formed on each side of the structure, one fluid entering through opening 19 and the other entering through opening 22. Suitable exits for the fluid can be formed by drilling a hole into the other end of the channel which would lie adjacent that part of the pattern represented as 23 and 24 of Figure 6.

In still another embodiment illustrated in Figure 9 a pair of heat exchangers or other similar articles can be made from a single sheet of metal such as 30. In this embodiment, sheet 30, which may be of a copper alloy similar to the utilized in the foregoing embodiments, has two grooves formed in the same surface thereof to divide the sheet into three areas 31, 32 and 33. It is to be noted that the width of area 33 is substantially equal or in excess of the sum of the widths of the areas 31 and 32. Patterns 34 and 35 of a suitable stop-off material such as utilized in the foregoing embodiment are applied to the surfaces of areas 31 and 32 and these areas are thereafter bent and pressed into contact with the surfaces of area 33. The resulting assembly is thereafter hot rolled and otherwise treated in accordance with the same process as described in the foregoing embodiments. By this process it is possible to make two structures from one sheet of metal as the structure resulting from the forge-welding of the adjacent surfaces of areas 31 and 33 and the forge-welding of the adjacent surfaces of areas 32 and 33 can be separated by slitting along the line formed by the abutting edges 36 and 37.

In the embodiment shown in Figure 10 a single sheet of metal is grooved and folded transversely. A folded edge across the width of the sheet is sufficiently strong to prevent relative movement of one area such as 40 with respect to the other area 41 for sheets of the more practical and common lengths. It is preferred in this embodiment, however, if the length of the sheet is much greater than the width, to introduce the folded edge 42 into the pinch of the rolls first. Hollow articles such as heat exchangers can be made from a sheet of metal folded in this way by employing substantially the same processing steps as described in the foregoing embodiments.

The method of this invention facilitates accurate regis-, tration of the various patterns with respect to each other. Indeed, one portion of a pattern may be placed on one surface of an opposing pair of surfaces and the remainder of the pattern be placed on the other surface. Moreover, duplicate patterns may be placed on each of the opposing surfaces to achieve greater pattern depth and to insure non-welding within that area.

Although several specific embodiments have been described in detail in the foregoing it is to be understood that such detail description has been presented solely for the purpose of illustration. For example, metal fabrications can be made in accordance with this invention from any other metal which can be forge-welded by a hot rolling process. Copper, copper base alloys including the one described hereinbefore, bronzes, brasses and aluminum are examples of metals suitable for the purpose. Any suitable stop-01f material which will prevent forgewelding of superposed surfaces of the sheet metal can be utilized. The surfaces to be welded must be clean. Any suitable method can be utilized for degreasing, cleaning and removing the oxide from these surfaces.

As indicated hereinbefore the pattern of stop-off material is foreshortened in the direction in which the assembly is to be hot rolled because the pattern elongates with the metal sheet. Although it is preferred to use a silk screen for applying the pattern to the sheet any other suitable means such as spraying, brushing, etc. may be utilized. The temperature at which the layers of metal are forge-welded for rolling will vary somewhat with the particular metal but for all practical purposes a temperature within about 100 C. of the recrystallization point of the metal is preferred. Under such conditions the various layers of sheet metal merge into one with a substantially complete erasure of any line of demarcation therebetween. The amount of reduction in one pass must be at least 35 per cent if copper alloys are utilized and at least 60 per cent if the metal is aluminum to completely erase the joint between the various folds of metal.

Many other variations in the foregoing embodiments will occur to those skilled in the art and can be made therein without departing from the invention except insofar as is limited by the appended claims.

What is claimed and desired to secure by Letters Patent is:

1. In the manufacture of hollow metal fabrications from sheet metal by a process which involves interposing a pattern of stop-off material between adjacent surfaces of sheet metal layers lying in face to face relationship, forge welding by rolling those areas not protected by the stop-off material, and thereafter inflating the unwelded areas by means of fluid pressure; the method of securing the sheet metal layers against relative slippage before and during rolling without spot-welding which comprises, grooving a single sheet of metal and bending and folding the sheet to provide the plurality of layers thereof lying in face to face relationship prior to forge welding.

2. The method of making a metal fabrication adapted to be inflated by fluid pressure to make a hollow article which comprises applying a pattern of stop-01f material, foreshortened in one direction on a metal sheet, bending and folding the sheet into layers lying in face to face relationship and having said pattern lying therebetween, and thereafter, while the resulting layers are secured against relative slippage by the folded edge and without any spot welding of the layers together for the purpose of preventing slippage, simultaneously elongating the assembly and welding those contacting surfaces of the layers bordering said pattern by hot rolling in the direction the pattern is foreshortened.

3. The process of claim 2 wherein said sheet is grooved and then folded along the groove.

4. The process of claim 3 wherein the thickness of the folded assembly is reduced in one pass at least 35 per cent by hot rolling.

5. The process of claim 4 wherein the metal sheet is aluminum and the thickness of the folded assembly is reduced in one pass at least per cent by hot rolling.

6. The process of claim 2 wherein said sheet is grooved and folded along an axis transverse to the direction of hot rolling.

7. The method of making a metal fabrication adapted to be inflated by fluid pressure to form a hollow article which comprises grooving a sheet of metal along a predetermined axis to divide the sheet into a plurality of substantially equally dimensioned areas, applying a pattern of stop-off material foreshortened in one direction to surfaces of alternate areas, bending said sheet along the grooves to form layers thereof lying in contacting face to face relationship and having interposed therebetween the pattern of stop-01f material, and thereafter, While the resulting layers are secured against relative slippage by the folded edge and without any spot welding of the layers together for the purpose of preventing slippage, simultaneously elongating the assembly in the direction the pattern is foreshortened and welding the contacting inner surfaces bordering the pattern by hot rolling in the direction the pattern is foreshortened.

8. In the manufacture of hollow metal fabrications from sheet metal by a process which involves interposing a pattern of stop-01f material between adjacent surfaces of superposed layers of said sheet metal and thereafter forge welding by rolling those areas not protected by the stopoff material; the step of securing the layers against relative slippage prior to and during said rolling without spot welding for the purpose of preventing slippage by bending and folding said sheet metal into a plurality of layers with said pattern interposed therebetween.

9. The method of making metal fabrications adapted to be expanded by means of fluid pressure which comprises forming two longitudinally extending grooves in a single sheet of metal such that the width of the area of the sheet lying between the grooves is at least twice the width of each of the substantially equally dimensioned areas lying on either side of said wider area, applying a pattern of stop-off material on the surface of each of the narrower areas, bending the sheet to fold the two narrower areas upon the wider area, and to interpose the patterns therebetween, and thereafter, While the resulting layers are secured against relative slippage by the folded edge and without any spot-welding of the layers together for the purpose of preventing slippage, simultaneously elongating the folded assembly in the direction the pattern is foreshortened and welding the contacting surfaces bordering the pattern by hot rolling in the direction the pattern is foreshortened, and severing the sheet where the edges of the welded layers meet.

References Cited in the file of this patent UNITED STATES PATENTS 1,265,940 Mooney May 14, 1918 1,938,633 Maskrey Dec. 12, 1933 1,940,850 Derby Dec. 26, 1933 1,979,539 Gardner Nov. 6, 1934 2,118,499 Durbin May 24, 1938 2,123,842 Cox July 12, 1938 2,212,481 Sendzimir Aug. 20, 1940 2,498,275 Johnson Feb. 21, 1950 2,662,273 Long Dec. 15, 1953 2,690,002 Grenell Sept. 28, 1954 

1. IN THE MANUFACTURE OF HOLLOW METAL FABRICATIONS FROM SHEET METAL BY A PROCESS WHICH INVOLVES INTERPOSING A PATTERN OF STOP-OFF MATERIAL BETWEEN ADJACENT SURFACES OF SHEET METAL LAYERS LYING IN FACE TO FACE RELATIONSHIP, FORGE WELDING BY ROLLING THOSE AREAS NOT PROTECTED BY THE STOP-OFF MATERIAL, AND THEREAFTER INFLATING THE UNWELDED AREAS BY MEANS OF FLUID PRESSURE; THE METHOD OF SECURING THE SHEET METAL LAYERS AGAINST RELATIVE SLIPPAGE BEFORE AND DURING ROLLING WITHOUT SPOT-WELDING WHICH COMPRISES, GROOVING A SINGLE SHEET OF METAL AND BENDING AND FOLDING THE SHEET TO PROVIDE THE PLURALITY OF LAYERS THEREOF LYING IN FACE TO FACE RELATIONSHIP PRIOR TO FORGE WELDING. 